Publications

The Cepu PSC operator ExxonMobil uses reservoir simulation to define resource size and to describe the optimal depletion plans for the carbonate fields. The simulator model depends on accurate description of the geology and flow units of the hydrocarbon reservoir and the aquifer that supports the field. Well correlation and seismic interpretation can describe the internal layering of the fields but the deeper units near the base of the hydrocarbon reservoirs are not penetrated by as many wells and are not imaged well by seismic due to distortion of the waves traveling through the high relief carbonate platforms. The simulated flow will be very different for geologic concepts that include a tight platform carbonate during early growth and the alternative model of high poroperm shallow water buildups. To better describe the early layers in the fields, ExxonMobil studied areas away from the fields on the Cepu carbonate platform that have better imaged early growth layers. This has resulted in an extensive paleogeographic description of the Cepu carbonate platform early growth systems and much higher confidence in recent geologic models of the fields. The Oligo-Miocene carbonate fields are high relief isolated platforms than grew vertically very fast near sea level as the basin subsided during post-rift subsidence following the Eocene rifting events. The main revelation of this study is that carbonates started growing before rifting ended and then coalesced after rifting stopped and subsidence accelerated. During the rifting interval, the water depth was variable between upthrown and downthrown blocks which resulted in nucleation of grainy buildups on the upthrown blocks and muddier deposition on the downthrown blocks and better exposure and dissolution of the upthrown block units. After rifting ended and the topography was healed, the buildups growing on the fault blocks either drown or coalesce into larger platforms that then grew vertically very fast to become the Cepu Block Fields. The ones that coalesced tend to be along the larger fault systems resulting in the dominant ENE – WSW orientation of the Cepu fields.